1. Field of the Invention
The present disclosure relates to an apparatus and a method for transmitting and receiving channel state information of a terminal that supports 256-state quadrature amplitude modulation (256QAM), and more particularly, to an apparatus and a method for transmitting and receiving channel state information that includes channel quality indicators (CQI) in order to support 256QAM in addition to three typical modulation methods, i.e., quadrature phase shift keying (QPSK), 16-state quadrature amplitude modulation (16QAM), and 64-state quadrature amplitude modulation (64QAM).
2. Description of the Prior Art
Information may be transmitted through a signal using signal properties such as intensities, frequencies, and phases thereof. Modulation is a process of transforming such signal properties into proper waveforms according to channel characteristics of a transmission medium. A digital signal may be used to transmit digital information by mapping the digital information to one of bit stream and a digitalized analog signal (sampled or analog-to-digital converted signal). Digital modulation is a process of transforming such digital signals (i.e., digital symbol sequences) to a proper signal according to the channel characteristics of a transmission medium. One of the typical modulation methods having high bandwidth efficiency is an M-ary QAM method that is expressed as 2M QAM, for example, QPSK (or 4QAM), 16QAM, or 64QAM.
The modulation methods of QPSK, 16QAM, and 64QAM are used for downlink data transmission in wireless communication systems such as Long Term Evolution (LTE) or LTE-Advanced. A base station transmits data to a terminal using such modulation methods, and the terminal receives data by demodulating transmitted signals.
Recently, an amount of data transmitted and received between terminals and associated base stations has been increased abroupltly due to sharp increase in the number of user terminals and in the data usage. This requires a modulation method that can rapidly process a large amount of data traffic.
Meanwhile, a base station selects one of the modulation methods by considering a downlink channel state, and informs an assocaited terminal of the same using downlink control information (DCI). The terminal identifies the received downlink control information, and performs demodulation of data corresponding to the modulation method to thereby receive the data.
To this end, the terminal measures the downlink channel state, and transmits information on the measured channel state to the base station. At this time, the terminal transmits CQI information included in the channel state information signal, which is mapped with QPSK, 16QAM, and 64QAM, to the base station. However, due to sharp increase in data traffic and data speed a new modulation method has been demanded. Furthermore, it has been also demanded for a method for indicating such a new modulation method in the CQI information having a limited size.